"Spots are on the surface of the solar body where they are produced and also dissolved, some in shorter and others in longer periods. They are carried around the Sun; an important occurrence in itself."- Galileo Galilei, 1611 AD

To the ancient Greeks, the perfect nature of the Sun was an inviolate belief. All astronomical bodies were in the realm of the gods and, therefore, were believed to be unchanging and unblemished by imperfections. The detection of sunspots on the Sun's surface destroyed this belief and opened up a fascinating new view of our Sun as both dynamic and volatile.

The Sun shows various signs of being active. The Sun has long-term variations such as the solar cycle with a peak of activity every eleven years. On shorter timescales, we see that the Sun also rotates about its axis. Sunspots and active regions appear around the Sun's eastern edge and disappear behind its western edge as the Sun rotates. We discussed solar rotation and solar cycles on Monday. Today we would like to concentrate on the short-term, or transient, changes which make the Sun so exciting.

Throughout the whole solar cycle -but most notably during times when the number of sunspots peak-the Sun creates major solar disturbances, or storms, which can have a significant effect on the Earth. These solar flares and coronal mass ejectionsoccur relatively rapidly, causing the Sun to shine brighter across the whole electromagnetic spectrum. Charged particles of immense energies are produced and are, on occasion, sent hurtling towards the Earth!